1. Field of the Invention
The invention relates in general to signal input devices and systems, and more specifically to such devices and systems which include a switch, and means operable by the switch to indicate actuation thereof.
2. Description of the Prior Art
In describing signal input devices of the prior art, it will be useful to describe a specific application of signal input devices in an elevator system. It will be apparent how certain problems associated with signal input devices in an elevator environment are also prevalent in other applications of such devices.
More specifically, in elevator systems car calls entered by passengers in the elevator car are generally entered on a car call pushbutton station which includes a pushbutton or switch for each floor the elevator car is enabled to serve. An incandescent lamp is associated with each pushbutton, with a lamp being energized when its associated pushbutton is actuated, to indicate to the passenger that the car call has been entered. A car call associated with an actuated button is sent to the floor selector and its associated control of the elevator car, and at some point during the answering of the car call the call is reset and the energized lamp associated with the car call is extinguished. The pushbuttons in the car call station are generally of the mechanical type in which a movable electrically conductive element makes ohmic contact with two spaced stationary elements, to complete an electrical circuit.
Each car call pushbutton and associated lamp generally has a wire in the traveling cable which interconnects the elevator car with the remotely located portion of the car control. This control includes the floor selector, as well as the control for the specific elevator drive utilized, such as the control for an A.C. or D.C. motor in a traction elevator system, and the control for a hydraulic cylinder, in a hydraulic elevator system.
Voltages of at least 100 volts are usually used in the car call pushbutton circuits, in order to break down any oxidation which may have formed on the electrically conductive elements, as well as to permit the use of low current incandescent lamps for the desired wattage or brightness level. A low current lamp permits relatively small common lamp return wires in the traveling cable, and variations in IR drop in the common lamp wiring in the relatively long traveling cable will have little or no adverse affect on the lamp brightness as additional calls are registered and their associated lamps energized.
The prior art car call control presents certain problems. The high voltage required at the pushbutton contacts is not compatible with solid state logic systems which are now being used to process car call signals, making it necessary to use high voltage to low voltage interface circuits between each pushbutton and the low voltage logic control. Further, the random failure of incandescent lamps, long a problem in the elevator industry, is especially pronounced when high voltage lamps are used because the long and delicate filament of the high voltage lamp is susceptible to early failure due to mechanical vibrations inherent in the operation of an elevator car. The failure of a single lamp may necessitate a special service call to replace the lamp. Further, the manufacture and assembly of the car call pushbutton station is costly, as the pushbuttons are manufactured as individual units which are manually assembled, aligned with openings in the cover plate of the station, and manually wired.